1. Field of the Invention
This invention in general relates to photographic camera apparatus, and, in particular, to scene light detecting apparatus for use with an automatic camera of the type having an electronic control system for receiving an input signal and controlling the firing of an electronic flash at a predetermined time after the initiation of an exposure interval.
2. Description of the Prior Art
Built-in light detecting devices which form an integral part of an automatic camera exposure control arrangement are well-known to those skilled in the photographic arts. Such light detecting devices generally consist of one or more photovoltaic or photoresistive type transducers associated with an optical system so that light from a preselected area of the scene to be photographed can be directed onto the photosensitive surface(s) of the transducer(s). An electrical output signal indicative of the intensity of the brightnesses of the various objects located in the preselected area of the scene is derived from the transducer(s) and is thereafter generally utilized to control the exposure delivered to the film in accordance with the sensitometric characteristics of the film and the known performance characteristics of the other elements which comprise the exposure control arrangement. The electrical output signal may be used prior to actual exposure to automatically adjust the exposure settings of the camera or may be used after an exposure cycle is initiated to terminate the cycle upon satisfaction of a predetermined exposure condition.
The preselected area of the scene depends on the "angle of acceptance" of the light detecting device; the "angle of acceptance" meaning the solid angle of the cone of light received by the light detecting device. Thus, if light from a particular scene object is to have an influence on the magnitude of the output signal of the light detecting device, that object must be located within the device's angle of acceptance, i.e., the object must be "seen" by the device. It is apparent therefore that the angle of acceptance of such light detecting devices can be used as a means for controlling what the exposure will be in the sense that it can be aimed at a certain area of the scene which is considered important in preference to another area of the scene which may not be considered quite as important.
However, what the angle of acceptance should be for a particular light detecting device depends on the kinds of scenes it will probably be used to measure and the type of lighting which is used to illuminate those scenes. Consider, for example, a horizontal landscape illuminated by skylight or sunlight. With this type of scene and lighting conditions, it is generally desirable to have a light detecting device which looks generally downwardly to exclude the sky whose influence, if considered, would tend to cause the ground details to be underexposed. As another example, consider a portrait scene illuminated with an artificial light source. In this type scene, it is generally desirable to have the light detecting device "look" straight ahead so as to receive substantially all the light reflected from the central part of the scene thereby exposing for proper fleshtones.
Those skilled in the art have recognized the important role that the angle of acceptance of such light detecting devices plays in controlling exposure and have described a number of light detecting devices by which the importance of different areas of a scene can be established via the device angle of acceptance. For example, in U.S. Pat. No. 3,511,142 issued to Conrad H. Biber on May 12, 1970 and entitled "Exposure Control Means", there is described an exposure control system which has a parameter which is modified in response to the attachment of a flash unit to a camera in which the exposure control system is incorporated. Specifically, attachment of the flash unit shifts a movable element into operative position relative to four photocells such that the fields of view (angles of acceptance) of the photocells are substantially congruent, each covering substantially the angular field of view of the camera. Under ambient lighting conditions (i.e., without a flash unit attached) the movable element is operatively positioned relative to the photocells so that each photocell is provided with a smaller angle of acceptance each of which is aimed at a different portion of the scene being photographed. With this arrangement, the angle of acceptance of each photocell is changed from a small solid angle when used in the ambient mode to a large solid angle when used in the flash mode thereby affecting a change in the sensitivity of each photocell in accordance with the size of its angle of acceptance.
Another example is described in U.S. Pat. No. 3,232,192 issued to Allen G. Stimpson on Feb. 1, 1966 and entitled "Photographic Exposure Measuring Device". Here an exposure control system is described which utilizes a plurality of photocells one of which is positioned to measure the intensity of skylight and others, each having a different acceptance angle, for viewing a corresponding different zone of the scene to be photographed. A pair of the photocells are fixedly aimed at different selected zones of the scene and their individual angles of acceptance, when combined, cover substantially all of the scene as defined by the angular field of view of the camera. No provision is made for preferentially exposing different zones of the scene by changing the angular direction in which the photocells are aimed at the scene. Instead individual zones of the scene are given preferential treatment by providing the photocells with different sensitivities and combining their outputs in an electrical arrangement by which a single output is generated to indicate or automatically regulate proper exposure.
Another example is shown in U.S. Pat. No. 4,173,400 issued to Faramarz Faramarzpour on Feb. 2, 1978 and entitled "Photographic Camera Apparatus". Here, an automatic camera having distinct ambient and flash exposure modes of operation is provided with a scene light detecting apparatus which has a predetermined angle of acceptance that, depending on the camera exposure mode, aims in different angular directions at a scene. This is accomplished by an arrangement that is responsive to the insertion of an artificial light source to aim the angle of acceptance above the camera horizontal axis.
The known prior art arrangements for changing the angle of acceptance of unicell devices is apparently restricted to cameras of the type which have distinct ambient and flash exposure modes of operation requiring some action on the part of a photographer, e.g., inserting of flash device or switching, to convert the camera from one operating mode to another and aiming the angle of acceptance is keyed to this action. However, cameras have been described recently which do not have distinct ambient and flash exposure modes that operate independently of one another and at the selection of the photographer. Such cameras are referred to as proportional fill-flash types and have exposure control systems that operate to control the firing of electronic quench type strobes under a range of natural lighting intensities such that film exposure is due to a mixture of available natural light and strobe light whose proportion changes in accordance with the intensity of the natural available light. Examples of such proportional fill flash systems are described in U.S. Pat. No. 4,192,587 entitled "Proportional Fill Flash" by A. LaRoque et al., issued Mar. 11, 1980, and U.S. patent application Ser. No. 074,993 filed in the names of Bruce K. Johnson et al. on Sept. 13, 1979 and entitled "Camera With Proportional Fill Flash Quench Strobe".
Since proportional fill flash type cameras do not require any selection on the part of a photographer which causes a camera to convert between different and distinct types of exposure modes, it is a primary object of the present invention to provide scene light detecting apparatus for use with such cameras and having an angle of acceptance which aims at different regions of a scene in a predetermined manner.
Another object of the present invention is to provide scene light detecting apparatus having an angle of acceptance which can automatically be aimed at different regions of a scene after an automatic camera exposure cycle has been initiated.
It is another object of the present invention to provide scene light detecting apparatus for use with proportional fill flash type systems to aim at different regions of a scene depending on whether film exposure is due primarily to natural light or strobe light.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter. Accordingly, the invention comprises the apparatus possessing the construction, combination of elements and arrangement of parts that are exemplified in the following detailed disclosure.